Rendering Backwards in Cycles
This Python script will step through your frames in reverse and render them one-by-one. Save as render-backward.py:

import bpy

for frame in range(bpy.context.scene.frame_end, 1, -1):
    bpy.context.scene.frame_set(frame)
    bpy.ops.render.render(write_still=True)


Run it like so:

blender yourfile.blend -b -P render-backward.py